This topic describes how to investigate why messages are
not being consumed at a destination on a service integration bus,
when the messages are being routed through a remote message point
and the consuming application is stopped.
About this task
Perform this task as part of either
Investigating why point-to-point messages are not being consumed or
Investigating why publish/subscribe messages are not arriving at a subscription. This task
explains how to investigate the flow of messages in a scenario where
the messages are being routed through a remote message point and the
consuming application is stopped.
The following
diagrams illustrate two possible scenarios. In Figure 1, ME2 is the
messaging engine that hosts the message point, and receives messages
from the producing application through ME1. ME3 is the messaging engine
that the consuming application is attached to, and hosts a remote
message point which represents the message point on ME2. In Figure
2, ME2 and ME3 host publication points that are represented by remote
publication points on ME1, where the producing application is attached.
Subscribing application B is connected to ME3 and receives messages
indirectly from ME1, via a subscription on ME2. a remote subscription
point on ME 3. These messaging engines are referred to in the following
steps.Figure 1. Point-to-point message consumption using
a remote message point
In the following figure, a bus contains three messaging
engines, ME1, ME2 and ME3. The publishing application is connected
to ME1 and the subscribing applications are connected to ME2 and ME3.
ME1 hosts remote publication points which represent the publication
points hosted by ME2 and ME3. Subscribing application B is connected
to ME3 and receives publications from ME1 through a remote subscription
on ME2.
Figure 2. Publish/subscribe messaging using
a remote message point 
Procedure
- If you have followed the steps in Investigating why point-to-point messages are not being consumed or Investigating why publish/subscribe messages are not arriving at a subscription before starting
this task, you should have displayed a list of message requests. On
the previous panel (runtime properties for the message point), check
that the Message requests issued (point-to-point
only) or Message requests received (publish/subscribe
only) value is greater than zero. If the value is not greater than
zero, no requests have been made. Check the consuming application
for errors:
- Check that the application is actually connected to ME2.
- Check that the application did not produce any errors which could
explain why messages are not being consumed.
- Check that the consumer was started.
- Check that the application did attempt to consume a message:
- If the application uses an asynchronous consumer, check that the
asynchronous consumer was registered.
- If the application is synchronous, check that the consumer performed
a 'receive' or a 'receive with wait' function (this may require a
modification to the application to extend the time that the application
waits for a message).
- If the number of issued message requests is greater than
zero, requests from ME3 to ME2 for messages on the message point have
been made. Check that the Completed message requests value
is greater than zero. If not, check that the two messaging engines
can communicate with each other, see Service integration troubleshooting: Checking the communication between two messaging engines in a bus.
- If the number of completed message requests is greater
than zero, requests are being issued by ME3, processed by ME2 and
completed back to ME3. To ensure that those requests were made by
the actual application being investigated, record the current values
of Completed message requests and either Message
requests issued or Message requests received.
Rerun the consuming application and check that both values have increased.
If the values do not increase, the application did not make a request
from ME3 to ME2 for this message point (the existing numbers relate
to a previous application that was consuming messages). Check the
consuming application for errors:
- Check that the application was started.
- Check that the name of the destination being consumed from is
correct.
- If the values do increase, the message request was issued
and completed, but no message was returned or processed by the consuming
application.
- Check that the application's selection criteria match the available
message or messages on the message point.
- Check that the application is correctly receiving the message,
by checking for application or runtime errors.
What to do next
If you are still having problems, contact your IBM® customer service
representative.